This invention relates to a mobile apparatus for continuous on-site testing and measuring of the reflectance of retroreflective roadway markers and other reflective materials such as painted and applied reflective striping materials.
Retroreflective pavement markers of the type disclosed in U.S. Pat. No. 3,332,327 are commonly used to delineate road edges and lanes and to provide other information to vehicle operators. The effectiveness of such pavement markers, as with other reflective materials, diminishes with use and weathering so that their reflectance decreases in time.
Specific roadway, traffic and other conditions also affect groups of markers on the same highway differently, and some groups of the markers may need replacement at different time intervals than others. Today, testing of the effectiveness of roadway pavement markers generally is accomplished by visual inspection, or, on a very limited basis, removing markers from the roadway for off-site testing at a lab facility. Moreover, lane-striping materials and painted lines are tested by stationary photometers which are positioned over the stripes, or by simple visual observation. Neither of these is an efficient way of determining the reflective qualities of those items for replacement purposes.
It therefore is a primary object of this invention to provide a mobile test apparatus for continuous on-site testing of the reflectance of pavement markers, reflective striping and the like.
Another primary object of the invention is to provide a mobile test apparatus for effective on-site testing of the reflectance of markers or the like which is capable of conducting such testing while moving along with traffic on the roadway, thereby to enable the testing to be conducted with a minimum of interruption of traffic flow and under substantially safe conditions.
It is a further object of the invention to provide a mobile testing apparatus which also will render an effective accurate record of the reflectance of all markers tested, so that, if desirable, only selected units may be replaced, depending upon the precise location of the defective units or the ineffective reflective or other striping materials.
Presently markers are laboratory tested according to standardized methods using a darkened room or tunnel in which a light source is directed at a reflector and the reflected light is received by a receptor. The distance from the source to the reflector and the reflector to the receptor is accurately controlled, as is the angular relationship between the incident and reflected light beams. Any changes in these distances and/or angles will substantially change the measured value of the reflected light and thus the determination of the unit's reflectance.
In any mobile testing apparatus it is also necessary to accurately control the source/marker-marker/receptor distances and angular relationships. For example, a mere two-inch vertical movement during operation of a movable test vehicle could result in a change in light path length which results in over a 50 percent error in the measured reflectance.
Prior attempts to provide mobile testing apparatus have not controlled such distances and angular relationships which change due to the movement and bouncing of the vehicle, and/or vertical curvature of the road. Thus, in prior devices, even though the marker may have been within desirable limits, the test apparatus could indicate an ineffective marker solely due to the changes in light path length. One prior device used "chopped light" for daytime testing and another used a shroud and is referred to as the "IRMA" device. One or more of these devices have other deficiencies such as a wide observation angle effect, graphic data display, and lack of control of test distance as the vehicle moved.
It is therefore another primary object of this invention to provide a test apparatus in which the length of the light path is maintained substantially uniform even though the testing vehicle, and thus light source, may move vertically relative to the roadway surface.
These and other objects of this invention will become apparent from the following description and appended claims.